Deep sea trenches could play a key role in climate change after ground-breaking experiments suggested they were 'disproportionately important'.

Probing the deepest part of the world's oceans - the Mariana Trench in the western Pacific - scientists found such underwater canyons trapped more carbon than previously thought.

The carbon cycle has been studied in other parts of the ocean, such as the abyssal plain - the large flat area of the ocean between 4.6km and 5.5km deep - but that of deep sea trenches has until now remained largely unknown.

Deepest spot: The Mariana Trench in the Pacific Ocean - recreated here - is around 11km deep and over 50km wide and contains canyons that trap more carbon than previously thought

Professor Ronnie Glud, from the University of Southern Denmark and the Scottish Association for Marine Science (Sams), said: 'Although these trenches cover just two per cent of the ocean, we thought they might be disproportionately important.

'It was likely that they would accumulate much more carbon because they would act as a trap, with more organic matter drifting to the bottom of them than in other parts of the ocean.'

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Professor Glud explained that preliminary data from his team's experiments suggested that trenches acted as 'traps'.

He said: 'Our results very strongly suggest that the trenches do act as sediment traps.

'And they also had high activity, meaning that more carbon is turned over by bacteria in the trenches than is turned over at 6,000m of depth in the abyssal plain.

Explorers: No one has visited the depths of the Mariana Trench since Don Walsh and Jacques Piccard in 1960

'What it means is that we have carbon storage going on in these trenches that is higher than we thought before, and this really means that we have a carbon dioxide sink in the deep ocean that wasn't recognised before.'

Now the researchers plan to evaluate how much carbon is stored compared to other parts of the sea to establish the role trenches play in regulating climate.

The international team - which also included scientists from the UK, Germany and Japan - used a lander to plumb the depths of the 10.9km-deep trench, with special sensors in a titanium cylinder.

It took three hours for the lander to fall to the seabed, where it carried out pre-programmed experiments.

Two explorers, Jacques Piccard and Don Walsh, previously reached the deepest part of the Mariana Trench - a point called the Challenger Deep - in 1960, but no humans have been back since.

Professor Glud told BBC News: 'This is the first time we have been able to set down sophisticated instruments at these depths to measure how much carbon is buried there.'

He added: 'Basically, we are interested in understanding how much organic material - that is all the material produced by algae or fish in the water above - settles at the sea bed, and is either eaten by bacteria and degraded or is buried.

'The ratio that is either degraded or buried is the ultimate process determining what are the oxygen and carbon dioxide concentrations of the oceans and the atmosphere, and this gives us an overall picture of how efficiently the sea can capture and sequester carbon in the global carbon cycle.'

Abyss: The Mariana Trench is the deepest place in the world's oceans

Dr Alan Jamieson, from Oceanlab, told the BBC the new study was helping researchers build a better idea of what happens in the deep.

He said: 'The trenches continue to amaze us.

'And to see an experiment such as this carried out at these extreme depths is a great leap forward in deep-sea science.

'These studies will greatly enhance our understanding of how the deep trenches contribute to carbon cycling in the world's oceans.'